Current conductor support



Sept. 13, 1938. 1.. s. NERGAARD CURRENT CONDUCTOR SUPPORT Filed Sept.18, 1937 INVENTOR LEON .5. IVERGAARD BY ATTORNEY.

' ductors.

Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE CURRENT CONDUCTORSUPPORT Application September 18, 1937, Serial No. 164,471

5 Claims.

This invention relates to means for supporting and sealing conductors ofalternating current in a wall such as the envelope of an electrondischarge device.

In power tubes large current carrying leads, such as the filamentconductors, are usually supported by cup-shaped bushings or thimbles ofmetal sealed along their rims to the glass wall of the envelope, theconductors passing centrally through the bottom of the thimbles. As thefilament leads usually enter the envelope side-byside, the current flowsin opposite directions in the leads and produces circularelectromagnetic lines of force surrounding each of the two con- Whenthese lines are produced by alternating current, they cut the walls ofthe thimbles and induce circulating currents and considerable heat loss.

An object of my invention is to make a bushing or thimble for lead-inconductors to minimize circulating currents and heat losses in thethimble induced by the currents flowing in the conductors.

The circular electromagnetic lines of force about each of two parallelconductors are, be-

cause of their mutual repulsion, eccentric with respect to thoseconductors. I have found that if the cylindrical walls of a thimblesurrounding the conductors are placed eccentric with the conductors andconcentric with the lines of force which cut the cylinder, circulatingcurrents and heating is reduced. As the circular lines of force collapseand expand about the conductors axial electromotive forces are inducedin the thimble. Since all points on each cutting line passsimultaneously through the wall of the thimble in my improvedconstruction, the net E. M. F. around any closed loop in the thimble iszero and no circulating current results. If the lines of force areirregular because of extraneous electromagnetic influence or because ofthree or more juxtaposed current carrying conductors, it is proposedaccording to my invention to so shape and space the side of thimble thatall points on each cutting line of force pass simultaneously through theside of the thimble.

The characteristic features of my invention are pointed out withparticularity in the claims and one embodiment is described in theaccompanying specification and appended drawing in which Figure 1 is asectional perspective view of my novel lead-in seal, and

Figure 2 is an end view of my novel lead-in seal showingdiagrammatically the magnetic field distribution.

The structural embodiment of my invention chosen for the purpose ofillustrating the characteristic features of my invention and shown inFigure 1 comprises a vitreous wall I representative of the envelope ofan electric device such as the wall of an electron discharge device withtwo conductors 2 and 3 passing through and sealed in the Wall bycup-shaped bushings or thimbles 4 and 5. The rims of the thimbles aresealed, preferably gas-tight, in the vitreous wall, which may be ofglass, and the conductors 2 and 3 may either be continuous metal rodspassed through openings in the bottom of the thimbles, or the conductorsmay be in two coaxial portions joined as by welding to opposite faces ofthe bottoms of the thimbles. The parallel conductors may be connected onone side of the wall to any desired circuit, or, in the case of a radiotube, they may be connected to electrodes in the tube. The conductorsmay serve, for example, to supply alternating current of high ampltiudeto a filament or they may function as the Lecher wire conductors of along line tuning system of a high frequency oscillator or amplifier.

The magnetic field distribution about two parallel conductors of thesame diameter carrying current in opposite directions is represented byelectromagnetic lines of force 6, Figure 2, each line being circular andeccentric with respect to the conductor which it encircles. If thetubular sides of the thimbles are concentric about the leads, themagnetic field strength will not be the same at each point on theperiphery of the thimbles and each line as it cuts the walls of thethimbles induces unequal voltages at each point on the thimbleperiphery. Since the induced voltages vary from point-to-point along theperiphery of the thimble, eddy currents and heating losses result.

According to the characteristic feature of my invention, the thimblesare so placed that their peripheries coincide and are concentric withthe cutting lines of force, the centers of thimbles being placed outwardon a line through the centers of the conductors so that induced voltagesare the same at each point on the periphery. It has been determinedmathematically that, if the conductors have equal diameters and thethimbles have equal mean diameters, the relation of the distance betweencenters of the conductors l1, the

distance between centers of the thimbles la, the diameter of the leadsd1, and the average diameter of the thimbles dz is From this relation,the distance between the centers of each conductor and its thimble mayreadily be calculated. If, however, the diameters of conductors 2 and 3are unequal, and are di and d2, the distance m1 between the centers ofthimble 4 and its conductor 2 and the distance m2 between the centers ofconductor 3 and its thimble 5 may be determined from the followingformulae:

in which Z is the distance between the centers of the two conductors, Lis the distance between the centers of the two thimbles and D1 and D2are, respectively, the diameters of the thimbles. If a third conductorlies parallel to conductors 2 and 3, the lines of magnetic force are nolonger circular, but are of an irregular shape, the only requirementaccording to my invention being that the wall of the thimble be soshaped as to coincide with the particular line of force cutting it.

My novel bushing or thimble for supporting the sealing lead-inconductors in a vitreous wall minimize circulating currents and heatlosses in the thimbles induced by currents flowing in the conductors.

I claim:

1. In combination, a wall, a plurality of alternating current carryingconductors extending through openings in said wall, means for supportingsaid conductors in said openings com prising cup-shaped thimbles withthe tubular sides of the thimbles joined to said wall in the opening,the bottom portion of each thimble being joined to one of theconductors, and said tubular sides of the thimbles being shaped tocoincide with electromagnetic lines of force cutting the tubular sides.

2. In combination, a plurality of cup-shaped thimbles with tubular sidesand a bottom portion, a current carrying conductor extending througheach of said thimbles and attached to said bottom portion, each point onthe sides of the thimbles being so spaced from the conductors as to besimultaneously cut by each electromagnetic line of force passed throughthe sides of the thimble by current flowing in the conductors.

3. In combination a wall, two parallel conductors extending through saidwall, two cup-shaped thimbles each being joined along its rim to thewall and at its bottom to one of said conductors, the center of eachthimble being spaced outwardly from the center of its conductor on aline through the centers of the conductors.

4. In combination a plurality of metal cylinders, an alternating currentcarrying conductor extending longitudinally through each of saidcylinders and supported in spaced relation to the sides of saidcylinders, the center of each conductor being displaced from the centerof its surrounding metal cylinder.

5. In combination, a wall, openings in said wall, metal cylindersattached to said wall in the openings, and an alternating currentcarrying conductor extending through each cylinder and supported inspaced relation to the sides of the cylinder, each conductor beingeccentric with respect to its cylinder.

LEON S. NERGAARD.

